The present invention relates to a valve timing control apparatus for varying opening and closing timings of intake and exhaust valves of an internal combustion engine in accordance with engine operating conditions.
A published Japanese patent application Publication (Kokai) No. 09(1997)-280018 shows a conventional valve timing control apparatus of a vane type.
The outline is described with reference to FIGS. 4 and 5. This valve timing control apparatus includes a timing sprocket 50 having a tooth portion 50a on the outer periphery, a tubular housing 51 fixed to the main body of the timing sprocket 50 by bolts 63. A rotor member 54 is fixed to one end of a cam shaft 52 by a bolt 64, and received rotatably in the tubular housing 51. The housing 51 has four of projections having a generally trapezoidal section projecting radially inwardly. On the other hand, the rotor member 54 includes four of vanes or blades 54a, 54b, 54c and 54d each separating an advance side hydraulic chamber 55 and a retard side hydraulic chamber 56 between two adjacent projections. Each of the vanes 54a.about.54d has a seal member for sealing between the advance and retard hydraulic chambers 55 and 56, by sliding on the inner circumferential surface of the housing 51.
The rotating member 54 is rotated in the forward and reverse directions by supplying and draining hydraulic pressure to and from the advance and retard hydraulic chamber 55 and 56 in accordance with engine operating conditions, to change the relative rotation phase of the timing sprocket 50 and the cam shaft 52 and thereby to change the opening and closing timing of an intake valve.
Between the vane 54a and the timing sprocket 50, there is provided a locking mechanism 57 for preventing or allowing relative rotation between the timing sprocket 50 and the rotating member 54.
This locking member 57 includes a pin sliding hole 58 formed in the van 54a along the axial direction of the cam shaft 52, a lock pin 59 slidable in this pin sliding hole 58 in a manner immune from the influence of the centrifugal force generated by rotation, and a latching bore 60 formed in the inner end surface of the timing sprocket 50. Moreover, the lock pin 59 is urged toward the latching bore 60 by the spring force of a coil spring 61. The lock pin 59 can disengage from the latching bore 60 by the aid of hydraulic pressure of an oil pump supplied to a pressure receiving chamber at the rear end of the pin sliding hole 58.
When the pressure of the oil pump is still low as in a starting operation of the engine, the lock pin 59 urged into the latching bore 60 by the coil spring 61 can prevent collision and tapping noise between the housing 51 and the rotating member 54 due to forward and reverse torque fluctuation of the cam shaft.
When the hydraulic pressure from the oil pump rises with increase in the engine rotational speed, the lock pin 59 moves out of the latching bore 60 by the increased pressure in the pressure receiving chamber, and thereby allows the rotating member 54 to rotate freely.